How can I return a value from a thread in Ruby?

Question

If I have the following code :

threads = [] (1..5).each do |i|   threads << Thread.new { `process x#{i}.bin` }  end threads.each do |t|   t.join   # i'd like to get the output of the process command now. end 

What do I have to do to get the output of the process command? How could I create a custom thread so that I can accomplish this?

Answer 1

The script

threads = [] (1..5).each do |i|   threads << Thread.new { Thread.current[:output] = `echo Hi from thread ##{i}` } end threads.each do |t|   t.join   puts t[:output] end 

illustrates how to accomplish what you need. It has the benefit of keeping the output with the thread that generated it, so you can join and get the output of each thread at any time. When run, the script prints

 Hi from thread #1 Hi from thread #2 Hi from thread #3 Hi from thread #4 Hi from thread #5 

Answer 2

I found it simpler to use collect to collect the Threads into a list, and use thread.value to join and return the value from the thread - this trims it down to:

#!/usr/bin/env ruby threads = (1..5).collect do |i|   Thread.new { `echo Hi from thread ##{i}` } end threads.each do |t|   puts t.value end 

When run, this produces:

Hi from thread #1 Hi from thread #2 Hi from thread #3 Hi from thread #4 Hi from thread #5